1. Field of the Invention
The present invention generally relates to a battery charger. More particularly, the invention relates to a modular battery charger system with charging control distributed among various modules. Still more particularly, the invention relates to a modular charger system with improved reliability and employing an improved method for determining a fully charged battery.
2. Background of the Invention
Although rechargeable batteries and battery rechargers have been available for years, significant room for improvement remains in this technology. Some rechargeable batteries are used in non-benign, outdoor environments. For example, land-based seismic survey equipment typically employs rechargeable batteries to power the data acquisition units used to acquire seismic data. These batteries, like all rechargeable batteries, must be recharged periodically. Normally, the batteries are removed from the equipment and connected to rechargers which are transported to the site being seismically surveyed. For some surveys it may be preferable to leave the recharging equipment in the field rather than transporting it to the field each time the batteries need charging.
As such, the rechargers are operated in an outdoor environment which often is harsh to the electronics comprising the recharger. The environment may include conditions such as high humidity, high or low temperature, rain, snow, or sleet. Such environmental conditions increase the likelihood of a failure in the charger. Field-based battery chargers typically are constructed to minimize the risk of the internal components becoming ruined from moisture and also to reduce damage to the unit occasioned by falling tree limbs, mishandling by field personnel and other factors. Although being able to easily maintain the recharger is important, conventional chargers are constructed more for durability than maintainability. That is, servicing such chargers usually is difficult to perform in the field. Thus, when a conventional charger fails, a technician is sent into the field to examine and, if possible, repair the unit. Often, however, the technician is forced to return the unit to a well-equipped, indoor service facility to make the repair, a procedure which is time consuming and costly.
Some field-based battery chargers are capable of charging more than one battery at a time. Such chargers usually have multiple charging circuits, each circuit capable of charging a single battery. Typically, if just one of the charging circuits in such a charger fails, the entire charger, including the remaining fully functional charging circuits, may have to be transported to a service facility to repair or replace the one malfunctioning circuit. Thus, because of one malfunctioning charging circuit, the entire charging capability of the charger is lost until the repair is completed. Accordingly, it would be desirable have a battery charger that, is highly reliable, and also can be repaired without losing the full charging capability of the unit while the failure is being corrected.
The desire for increased reliability also applies to battery chargers that are used indoors in a more benign environment where the possibility of a malfunction still exists. In many indoor applications, battery chargers may be used in time critical events such as related to the use of medical equipment in a hospital in which battery and battery charger "down time" should be minimized.
Another aspect of reliable battery charging involves determining when a battery has been fully charged. Determining the "end of charge" condition prevents a battery from being over-charged, a condition that can damage certain types of rechargeable batteries. Many conventional end of charge determinations are based on measuring the voltage of the battery and determining when the voltage meets or exceeds a predetermined threshold. Often, such voltage-based end of charge protocols are inaccurate because of a particular battery's chemistry. Such inaccuracies may cause a battery to be under-charged (i.e., not be fully charged) or be over-charged to a certain extent. Thus, a more accurate, reliable method for determining the end of charge condition is needed.
Accordingly, it would be desirable to have a battery charger that provides greater reliability and maintainability than with conventional chargers and can more precisely charge a battery to full capacity. Despite the advantages that such a charger would offer, to date no such charger has been introduced.